Only one species of penguin currently waddles along Australia’s southern coast, a semiaquatic bird that is the smallest of all its family and so tiny that it’s commonly known as the little or fairy penguin. But in the deep past a greater variety of much more imposing birds populated this coast. Now, thanks to the fossil record, paleontologists have discovered that Australia was a refuge for penguin giants.
Penguins are pretty ancient for birds. The oldest, the genus Waimanu from New Zealand, evolved shortly after the mass extinction that wiped out its non-avian dinosaur relatives about 66 million years ago. From there, penguins proliferated throughout the southern hemisphere, but Australia has always represented a gap in the broader pattern.
“Australian fossil penguins have, until now, been left out of discussions of global patterns of penguin evolution,” says Monash University paleontologist Travis Park, “probably mostly due to the fact the fossil record is a lot more fragmentary [there] than elsewhere.” By sorting through those pieces and comparing them to what’s known from other places, however, Park and his colleagues have now figured out Australia’s role as a holdout for some of the last of the world’s oversize penguins.
Australia was not a prime center for penguin evolution, Park and his colleagues report April 26 in PLOS One. Instead, the continent was a place where different penguin lineages landed and then went extinct. The continent hosted an ongoing turnover of various penguin species over the past 66 million years, including some of the final ancient giants.
The last of these giants was Anthropodyptes gilli, a species known from only an upper arm bone. Because these big birds and their giant brethren are only known from fragments, scientists can only guess at what they may have looked like. But, Park says, based on more complete fossils found elsewhere, the largest of these birds would have stood somewhere between 4.2 and 4.9 feet tall. That’s a bit taller than the tallest penguins now alive, the emperor penguins.
All giant penguins went extinct by about 23 million years ago, Park says, except for Anthropodyptes, which survived until some 18 million years ago. Whether this bird was the descendant of earlier giants or independently gained its large size from small ancestors isn’t clear. Either way, this bird would have been almost tall enough to look you in the eye and was a remnant of an earlier age of giants that had closed everywhere else.
But how did Australia go from being the last refuge of huge penguins to home to just one tiny species today? The continent’s shifting place on the map might be the reason. The Australian and Antarctic plates once butted up against one another. “Since Australia split from Antarctica in the Cretaceous, it has been slowly drifting northwards, forming the Southern Ocean” in between, Park says. As the gap between the two continents got wider and wider, it became more and more difficult for penguins from Antarctica—or anywhere else—to reach Australia.
“Sheer isolation,” Park says, provided prehistoric penguins a respite and also explains why only the fairies are left to waddle across the same beaches.